1. Field of the Invention
The present invention relates to a silver halide photographic light-sensitive material having improved image sharpness and resistance to stress.
2. Description of the Related Art
Normally, in a photographic light-sensitive material comprising a silver halide emulsion layer, light scattering caused by silver halide grains tends to reduce the sharpness of the emulsion layer.
U.S. Pat. Nos. 4,434,226, 4,439,520, and 4,433,048 describe that image sharpness and the like can be improved by use of a tabular silver halide emulsion and that this technique can be applied to a photographic light-sensitive material.
However, tabular silver halide grains have poor resistance to stress, and form many stress marks and therefore results in difficulties in designing photographic light-sensitive material, as will be explained below.
More precisely, a photographic light-sensitive material on which is coated a silver halide emulsion is subjected to a variety of stresses when in the form of a conventional photographic negative film; being rolled up inside a cartridge, bent when it is inserted into a camera, and pulled when it is wound and re-wound.
On the other hand, a sheet-like film such as a light-sensitive print material or a roentgen light-sensitive material for medical and direct X-ray often becomes bent or folded on account of it being handled directly by an operator.
In addition to the above, all light-sensitive materials are subjected to high stress when cut and during manufacture.
When a photographic light-sensitive material is subjected to such stress, silver halide grains are stressed through gelatin which is a binder of the silver halide grains, or through a plastic film which acts as a support therefor. When the silver halide grains undergo such stress, the photographic properties of the photographic light-sensitive material are changed, as is described in detail in K.B. Mather, J. Opt. Soc. Am., 38, 1054 (1948), P. Faelens and P. de Smet, Sci. et Ind. Phot., 25, No. 5. 178 (1954) P. Faelens. J. Phot. Sci, 2, 105 (1954).
Consequently, there is widespread demand for a photographic light-sensitive material whose photographic properties are not adversely affected by any type of stress.
In order to improve resistance to stress, a plasticizer such as a polymer or emulsion is added, or the ratio of silver halide to gelatin in the silver halide emulsion is reduced so that no stress reaches the grains.
For example, British Patents Nos. 738,618, 738,637, and 738,639 disclose methods of using a heterocyclic compound, alkylphthlate, and alkylester, respectively; U.S. Pat. Nos. 2,960,404 and 3,121,060 disclose methods of using polyhydric alcohol and carboxyalkylcellulose, respectively; JP-A-49-5017 discloses a method of using paraffin and a carbonic acid salt; and JP-B-53-28086 discloses a method of using alkylacrylate and an organic acid. Hereinafter, the symbol "JP-A-" will be used to denote a Japanese Patent Disclosure, and the symbol "JP-B-" will be used to designate a Japanese Patent Publication. Further, the symbol "JP-A-(examined)" will be used to specify a published Japanese patent application without having been laid open which was filed before Jan. 1, 1971 when the system of laying open any patent application came into existence.
However, since mechanical strength of an emulsion layer is reduced when a plasticizer is added, the amount of the plasticizer which can be used limited. In addition, when the amount of gelatin is increased, sharpness is degraded or a developing speed is reduced. Therefore, neither of these methods can achieve a sufficient effect.
As a method of improving resistance to stress of the tabular silver halide grain itself, JP-A-59-99433 discloses a method of forming an iodide rich annular region inside a grain.
Although resistance to stress can be improved by this method, further improvements are desired.